A few months ago I took my 90' 740GLE car to the dealer. It had been hard to start, and hard to keep running once started. The dealer cleaned the knock sensor, but said the car had rod knock and that I should be looking to get rid of it before the engine went out. (To their credit, they weren't trying to take more money from my pocket. They discouraged me from having any more work done on the car.) People here told me that it was more likely piston slap, and that I should get a second opinion at an independent Volvo shop. I got it back from there today. The mechanic drove the car around for about 10 days, and never could reproduce my problem. He said that the noise wasn't rod knock or piston slap, but just a hydraulic lifter, and after a little "hard use of the engine" that noise disappeared and didn't come back. He did see, though, that the car badly needed a tune up; the spark plug wires looked old enough to be original. I suspect that needing a tune up was a major cause of the car's earlier problems. (Until a couple of months ago the car was my wife's. She took it to the dealer for all of its scheduled maintenance, so I assumed that things like tune ups were getting done. Still, I have to admit I'm not a car guy.) I was ready to ditch my brick, which I just inherited when we got my wife a new Sonota. Now I figure it may at least see 200K. (26K left to go; I guess 174K isn't bad for a 16 cylinder.) He told me it needed a couple of bearings (left wheel, drive shaft); I am going to drive it for a month to make sure it is really running well, then have those replaced. Thanks, all.